The present invention relates to a DC power supply device, and more particularly to a double usage DC power supply device which can be used indoors as well as in a car to convert city power supply or car battery power supply into desired DC power supply.
A notebook computer is equipped with a rechargeable battery. However, the battery can only provide the notebook computer with the necessary working voltage for a limited length of time. When the power of the battery is low, the notebook computer cannot function well, and a power supply device may be used. There are two known types of power supply devices, namely, the first type for connection to a city power supply outlet, and the second type for connection to a car battery power supply circuit. The first type is an AC to DC power inverter. The second type is a DC to AC power inverter. As illustrated in FIG. 1, the power supply device (AC to DC power inverter) 8 comprises a plug 81 for connection to a city power supply outlet to receive AC power supply from it, and a DC output connector 82 for connection to a power input connector of a notebook computer to provide it with desired DC power supply. A DC to AC power inverter cannot be directly connected to a notebook computer, and must be used with an AC to DC power inverter. As illustrated in FIG. 2, the power supply device (DC to AC power inverter) 9 comprises a plug 91 for connection to a socket for cigarette lighter of a car to obtain DC power supply from it, and a socket 92 which receives the plug 81 of the power supply device (AC to DC power inverter) 8 to provide it with AC power supply, permitting AC power supply to be converted into DC power supply and then sent to the notebook computer which is connected to the DC output connector 82 of the power supply device (AC to DC power inverter) 8. It is inconvenient to carry these two types of power supply devices for use with a notebook computer in a car.